HOST-PARASITOID FOOD WEBS - DYNAMICS, PERSISTENCE, AND INVASION

We study the population dynamics of a model host-parasitoid community containing two hosts that interact only through a shared generalist pa rasitoid. Each host is also attacked by a specialist parasitoid, makin g a community of up to five species of insects. Information from host- parasitoid community ecology is used in deciding how these species int eract. By considering both community stability and whether absent spec ies can invade, we predict which communities occur in different region s of parameter space. A crucial determinant of community structure is the relative searching efficiencies of specialists and generalists and the nature of the density-dependent reduction in parasitoid searching efficiency. In some areas of parameter space, there is no dynamically stable end point, and complex cycles occur where the food web structu re is constantly changing, species being added through invasion and lo st through direct and indirect competitive interactions. We also find that whether a species is able to invade can depend on the interaction between its dynamics and that of the resident species. We conclude th at some communities of hosts and parasitoids may display complex dynam ic behavior determined by both local population interactions and the f requency of species invasions.